Benzothiazyl disulfide-diarylguanidine derivatives



Patented Nov. 4, 1947 UNITED STATES PATEN OFFICE nENzo'rHIAzYL msilfi innfhihifiil- GUANIDINE DERIVATIVES Arnold R. Davis, Riverside, Gonin, assign'or to American Cyanamid Company, New York, N. Y-., a corporation of Maine No Drawing. Application February 8, 1945,

Serial No. 576,908

4 Claims.

This invention relates to a novel vulcanization accelerator, to rubber compositions containing the same and to methods of vulcanization using these accelerators. More specifically, the invention relates to novel activated accelerators which constitute fusion products of benzothiazyl disulfide and a diarylguanidine.

For many years, natural rubber and, more recently, synthetic rubber has been vulcanized using as the accelerator benzothiazyl disulfide activated by a diarylguanicline and metal oxides, such as zinc oxides and the like. Benzothiazyl disulfide produces excellent results so far as the physical properties of a properly finished product are concerned. While its use has been quite extensive, improvements have been constantly sought.

Benzothiazyl disulfide has only a very low solubility, less than 0.5%, in rubber at ordinary room temperatures. This leads to a number of difficulties. Compounds which have such limited solubility in rubber as exhibited by benzothiazyl disulfide are extremely difiicult to disperse uniformly in the composition. This has the unfortunate efiect of producing uneven cures. Poor accelerator distribution results in non-uniform test results and erratic performance in service. This difficulty is aggravated by the ordinary procedure in the plant. Rubber compositions during milling are at elevated temperatures, usually above 60 C. and often at about 100 to 160 C. While the benzothiazyl disulfide may be thoroughly dissolved in the rubber at the high temperature, it is precipitated out when the material cools. In some cases, crystals may even be observed at the surface.

When a compound such as benzothiazyl disulfide is used with another compound to form the actual accelerator, as in the present instance it is used with a diarylguanidine, stillfurther difficulties are encountered. Not only is the material poorly distributed, but, because of the neterogeneous mixing, the chemical reaction between the components of the accelerator is also indifferently accomplished. Again, wide variations in tensile strength, elongation and other physical properties are to be noted in test samples and the products are erratic in service.

It is, therefore, the principal object of the present invention to provide a novel accelerator "which will possess the natural advantages inherent in theuse er activated behzothiazy'l dislilfid'e "Without being subject to the d-ifiiculties encountered when the latter is used per se with activators. invention to provide an accelerator which is simply and readily made, which is easily cem- "poenaea with the vulcahizabl'e composition, and which gives uniform and' i-i'nprov'ed physical prop erties to the vulcanized roduct.

general, the desired objects or the present invention are simply 'ai-ld easily a complished by recognizing that the essentialdifliculty is either one of distributing or one of forming the acce1-' erator in the compound. The distributional difficulties are overcome by the use of the novel activated accelerators of this invention. The latter constitute amorphous chemical reaction products obtained by the fusion of benzothiazyl clisul-fide and a diaryl'g'uanidine having one mononuclear aryl substituent on each of "the amino nitrogens in accordance with the formula in which R and 'R." represent the aryl radicals.

The diarylguanidine used in preparing the novel accelerators of the present invention is not necessarily limited 'to any particular choice. Excellent results are obtained, for example, using such mononuclear substituted guanidines as diphehyl guanidine, the di -tolyl g'uanidines, phenyl, o-tolyl guanidine, and the dixylyl guanidines. In choosing the particular guanidine to be used, certain precautions should be noted. The dixylyl guanidines when fused alone with benzothiazyl disulfide yield products which exhibit definite crystal phases. Diphenyl guanidine if heated alone With benzothiazyl disulfide at too low a temperature may yielda product showing some crystalline phases. While the formation of crystal phases shows the products are actually chemically combined and not simple mixtures, in use, crystalline forms are not as satisfactory as the amorphous forms. The other diarylguanidines produce substantially amorphous fusion products and cause no trouble in this respect. Where the use of dixylyl guanidines is desirable, the tend ency toward crystallization can be readily elin'i It is also an object of the present 3 inated by using them in admixture with another diarylguanidine, preferably a ditolylor a phenyl, tolyl guanidine.

The exact proportions of benzothiazyl disulfide of diarylguanidine used is not wholly critical. In the experimental work done in the development of the accelerators of the present invention, the most preferable results were obtained using a molal ratio of 1:2. These proportions also simplify calculation when it is desirable to use one of the materials which produce products having crystalline phases. One mol of the crystal-producing guanidine, one mol of the non-crystalproducing guanidine and one mol of the benzothiazyl disulfide are readily combined. When combined, the product has excellent properties. These proportions, however, may be varied by a few percent in either direction without neces'' sarily producing an adverse effect on the vulcanized product. The preferred amorphous products have shown complete solubility even when used to the extent of 3% on the rubber.

Actual preparation of the novel accelerators of the present invention is quite simple. The selected materials, usually in, comminuted form, are admixed, the mixture is heated to the fusion temperature and the temperature is held at that point for a short time. The mixture becomes fluid before the maximum temperature is reached. After a few minutes at fusion temperature, the fluid becomes a clear liquid, indicating the occurrence of some chemical change. Fusion temperatures of 120 -150 C. normally cover the expected range.

With the exception of the use of dixylyl guanidines alone, or the use of diphenyl guanidine at too low a temperature, all the fusion products on cooling yield clear, resinous products, which are free from crystalline material. After cooling, all the amorphous products soften at a lower temperature than that at which the mixture of original materials became fluid.

While its exact nature is not wholly understood, the fact that a chemical change occurs during fusion is evidenced in several ways. First, as noted above, the fluent material becomes clear during fusion. Second, the fusion product is completely soluble in rubber, whereas only the diaryl guanidine component of a mechanical mixture dissolves freely, only a small amount of the benzothiazyl disulfide going into solution. Third, a composition containing the fusion product, after curing, possesses much better physical properties than those of vulcanizates from compositions containing only a mechanical mixture.

The invention will be more fully described in conjunction with the following specific examples which are illustrative only and not by way of limitation. All parts are by weight unless otherwise noted. In the examples, the following symbols are used:

BTDS=benzothiazyl disulfide DPG=diphenyl guanidine DOTG=di-o-tolyl guanidine DXG=dixylyl guanidines POTG=phenyL o-tolyl guanidine GR-S=Government Rubber-styrene EXAMPLE 1 Two mol parts of DPG and one mol part of BTDS were admixed, melted and fused at about 125 C. for several minutes, after the melt became clarified. After cooling a clear amorphous resin softening at 55-60 C. is obtained. Some A mixture of one mol part each of DXG and 5 BTDS was heated to 150 0. in 17 minutes and held at 145-150 C. for 8 minutes. The resultant liquid was clear in a thin film but after cooling a considerable quantity of fine crystals was apparent. The product softened at about 66-7 1 C.

As was pointed out above, fusion products exhibiting crystal phases are not as satisfactory for use in vulcanization as are the properly prepared amorphous reaction products. As was also pointed out, such tendency to produce crystalline phases is obtained under two conditions. When diphenylguanidine is used alone as the only diarylguanidine, the fusion, if carried out at too low a temperature, may produce a reaction product exhibiting some crystalline phases. This is readily overcome by heating at a higher temperature. This is shown clearly by the following example.

EXAMPLE 3 Example 1 was repeated, heating the mix to 150 C., in 23 minutes and holding it at 145-150 C. for 5 minutes, the cooled product was found to be amorphous, softening at 52-57 C.

EXAMPLE 4 Two mol parts of DOTG were fused at about 130 C. with one mol part of BTDS. The resultant product was an amorphous resin softening at 60-65 C. and free from crystalline material.

EXAMPLE 5 One mol part of DOTG and one mol part of DPG were fused at about 130 C. with one mol part of B'IDS. The resultant product was an amorphous solid softening at 57-62 C.

As was noted above, the other condition under which crystalline phases are likely to be obtained is when dixylylguanidin is used as the only diarylguanidine. Where it is desirable to use dixylylguanidine, this tendency to produce crystalline phases, shown above in Example 2, may be readily overcome by using therewith an equimolar proportion of a non-crystal-producing guanidine such as diphenylguanidine or di-otolyl-guanidine. This is illustrated in the following examples.

EXAMPLE 6 One mol part each of DPG, DXG and BTDS were mixed and heated to about 130 C. over 15 minutes and then held at -130 C. for 5 minutes. The clear amorphous product softened at 63-68 C.

EXAMPLE '7 One mol part each of DOTG, DXG and B'I'DS heated to C. in 20 minutes and held at that point for about 5 minutes yielded a product on cooling which was amorphous and softened at 64-69 C.

EXAMPLE 8 One mol part each of DPG, POTG and BTDS heated to 140 C. in 20 minutes and held at -140 C. for five minutes and cooled produced an amorphous product softening at 56- 61 C.

EXAMPLE 9 A mixture of one mol part each of DOTG, POTG and BTDS heated to 125 C. in. 15 minutes, held at 125 C. for minutes gave on cooling an amorphous product melting at 59-64 C.

EXAMPLE 10 The accelerator activity of the products of the present invention may be illustrated as follows. Two portions of a butadiene-styrene copolymer synthetic rubber (GR-S) were compounded and vulcanized, and the resultant physical properties of the vulcanizate tested. In the first, the fusion product obtained in Example 4 was used as the accelerator, and in the second, a diphenyl guanidine-benzothiazyl disulfide fusion product of Example 1 was used. The composition and the resultant properties of the vulcanizate are shown in the following table:

Set-up Tests $2 2 3? a 100 0. inches No Heat 0.134 After 2.5 hrs. in Boiling H O 0.161 Change, per cent SHORE HARDNESS (0.5"w30" Minutes Cure at 141 C. dwell) PHYSICAL TESTS Modulus at 200% Elongation Tensile strength Elongation, per cent Set, per cent Modulus at 200% Elong Tensile Strength Elongation, per cent l. 380

The unpredictable benefits obtained by reacting the components of the activated accelerator before the rubber compounding is readily illustrated by the following example:

EXAMPLE 12 Three additional samples of GR-S were compounded. In the first of these samples, the activator and the accelerator were separately added. In the second, a fusion product prepared according to Example 3 was used, and in the third, 'a phenyl-o-tolyl guanidine benzothiamyl disulfide fusion product was used. In order that the un- Table I Compounds 2 2 10 10 -BTDS Fusion Prod 1. 20 DPG-BTDS Fusion Prod 1.30

S T t Williams 3 min. 'Y

6 up es s at 100 0. inches N0 Heat 0.116 0115 After 2.5 hrs. in Boiling H2O. O. 146 0. 152 Change, per cent +26 +32 85 SHORE HARDNESS Minutes Cure at 141 C. (0.530 dwell) PHYSICAL TESTS 60 Cure at 141 0.

Modulus at 200% Elongation 1 475 500 Tensile strength 2, 900 3, 225 Elongation, per cc 620 625 Set per cent..- 25 25 Torsional hysteresis a 0.148 0. 150

After 48 hor s. Aging at Modulus at 200% Elong. 1, 050 l, 025 Tensil strength 2, 750 2, 825 Elongation, per cent 520 400 1 Modulus and Tensile in lbs/sq. in. 2 Set at Break 2 min. after break.

EXAMPLE 11 A similar procedure was carried out on a third sample, using as the accelerator a fusion product obtained according to Example 5. The proportions used and the results obtained are shown in the following table:

Table II Compound 0 Coal Tar Softener DOTG-DPG-BTDS Fusion Prod the present invention.

(The lowest percenta e change in the Y value indicates the lowest tendency to scor or procure.)

SHORE EARIDNESS tures. This practice may be illustrated by the procedure of the following example:

EXAMPLE 14 Two GR-S compositions were prepared, in the first of which 0.9% of the accelerator produced according to Example 5 was used. In the second, 0.6% of this accelerator was used in conjunction with 0.25% of BI'DS. The ingredients used and the physical properties of the product are shown in the following table: f

45 Minutes Cure at 141 0 65-59 65-58 64-57 Table V TENSILE TESTS 15 Compounds 45' Core at 141 0., Unaged G H 750 725 700 GR-S. 100 100 Tensile Strength 2, 400 2, 900 2, 800 E'PC lack 50 50 Elongation, per cent. 435 52 505 gig? Oxide 5 5 ur 2 2 Coal Tar Softener 5 5 DOTG-DPG-BTDS Fusion Prod 0. 9 0. 60 BTDS v0.25

Modulus Tensile Strength PHYSICAL TESTS Elongation, per cent 3 350 60 Cure at 1 Modulus (at 200% along.) and tensile in p. s. 1. 141 0.

While the foregoing discussion has been largely M d 1 1 limited to examples usmg synthetic butad1ene T i,S ,,Zg%{,' 1 3, 328 323 styrene copolymer type rubbers, this has been Elongation, P cent 650 645 The novel acsimply for illustrative purposes. celerators of the present invention and the use thereof are applicable not only to synthetic vulcanizable polymers other than the butadienestyrene polymer but also to natural vulcanizable rubber. This is illustrated in the following example.

EXAMPLE 13 A procedure similar to Example 6, using natural rubber and an accelerator produced according to Example 2 was carried out. The proportions used and the properties of the product are shown in the following table.

Table IV Natural Rubber 100 Whiting 70 Clay 9 Furnace Black 8 EPC Rlack 2 Asphalt Base Oil 3 Zinc Oxide 5 Sulfur 2.25 DPG-DOTG-BTDS Fusion Prod 1.35

TENSILE TESTS 25' Cure at 130 C.

Modulus at 300% 850 Tensile Strength 1 2,825 Elongation, per cent 560 Pounds per square inch.

1 Pounds per square inch.

I claim:

1. As a new composition of matter, a low-softening point, amorphous, reaction product, prepared by admixing one mol part of benzothiazyl disulfide with about two mol parts of a member selected from the group consisting of the ditolyl guam'dine, phenyl, tolyl guanidine, diphenyl g uanidine, mixtures thereof and mixtures containing at least one of these guanidines and a dixylyl guanidine in which the dixylyl guanidine content does not exceed about 50 mol percent; heating the mixture to fusion temperature, in the case where diphenylguanidine is the only diarylguanidine used, the temperature used being above about 0.; holding the fused mixture at about the fusion temperature for about 1-15 minutes after the melt becomes clear and cooling the product to room temperature.

2. As a new composition of matter, an amorphous, low-softening point, reaction product, prepared by admixing one mol part of benzothiazyl disulfide with about two mol parts of mononuclear 1,3 di-o-tolyl guanidine; heating the mixture to fusion temperature; holding the fuzed mixture at about the fusion temperature for about 1-15 minutes after the melt becomes clear and cooling the product to room temperature.

3. As a new composition of matter, an amorphous, low-softening point, reaction product, prepared by admixing one mol part of benzothiazyl disulfide with about two mol parts of 1- phenyl, 3-o-tolyl guanidine, heating the mixture to fusion temperature; holding the fused mixture at about the fusion temperature for about 1-15 minutes after the melt becomes clear and cooling the product to room temperature.

4. As a new composition of matter, an amorphous, low-softening point, reaction product, prepared by admixing one mol part of benzothiazyl disulfide withabout one mol part of mononuclear 1,3 diphenyl guanidine and about one mol part of mononuclear 1,3 di-o-tolyl guanidine; heating 9 10 the mixture to fusion temperature; holding the UNITED STATES PATENTS fused mlxture at about the fuslon temperature for about 1-15 minutes after the melt becomes clear umber Name Date and cooling the product to room temperature. 1,393,346 Soott J an. 10, 1933 ARNOLD DAVIS, 5 1,936,562 Kilbourne, Jr. Nov. 21, 1933 REFERENCES CITED FOREIGN PATENTS The following references are of record in the Number Country Date file of this patent: 413,296 Great Brltam July 10, 1934 

